Recently, secondary batteries are widely used for electric automobiles which secure driving force by using an internal combustion engine and/or an electric motor, as well as miniaturized apparatuses such as portable electronic apparatuses. The electric automobiles include hybrid automobiles, plug-in hybrid automobiles, and pure electric automobiles which are driven by only an electric motor and a battery without an internal combustion engine.
In the case where a secondary battery is used for the electric automobile, lots of secondary batteries are electrically connected in order to increase capacity and power. Particularly, a pouch type secondary battery is widely used for medium and large apparatuses due to an advantage in easy stacking.
The mechanical rigidity of the pouch type secondary battery is not high because the pouch type secondary battery is generally packed with a battery case of a laminated sheet including aluminum and a polymer resin. Therefore, when a battery module including a plurality of pouch type secondary batteries is configured, a cartridge is generally used in order to protect the secondary battery from external impact, etc., prevent moving of the secondary battery, and facilitate stacking.
A plurality of cartridges each storing a pouch type secondary battery are provided such that the cartridges are mutually stacked, and the battery module may include the plurality of stacked secondary batteries and cartridges.
A pouch type secondary battery performs charging or discharging through an electrochemical reaction. When heat generated during the charging/discharging process is not effectively dissipated, temperature inside the secondary battery may rise rapidly. The rapid rise in the temperature causes a decomposition reaction of an electrolyte and thus generates gases inside the secondary battery.
In this case, a swelling phenomenon, which is a kind of an inflating phenomenon, may occur due to an increase in internal pressure of the battery case, and furthermore, when the swelling phenomenon becomes severe, a serious problem such as an explosion of the secondary battery may occur.
Therefore, the pouch type secondary battery is generally designed such that when internal pressure of the battery case reaches a preset pressure or more, sealing of the battery case is released and gases are discharged to outside.
Meanwhile, a battery pack of an electric automobile is configured such that gases are not introduced into a compartment even when the gases are generated from the secondary battery. For example, as illustrated in FIG. 1, a battery module 2 including a plurality of secondary batteries and cartridges according to the related art may be sealed by an external pack case 1. Therefore, in the case where gases are generated from the battery module 2, the gases are locked in the external pack case 1. Also, when internal pressure of the pack case 1 rises, a gas outlet 3 provided to one side of the pack case 1 is open and may discharge the gases to the outside of the pack case 1. In this case, since the gas outlet 3 is connected to an exhaust line of an automobile, the gases may be safely discharged to the outside of the automobile along the exhaust line.
However, since a battery pack used for medium and large apparatuses such as electric automobiles includes intensively configured battery modules in order to provide high power, a volume and weight thereof increase more and more. The size of the battery pack increases more and more, but a space inside an electric automobile in which the battery pack may be installed is limited.
Therefore, to efficiently install a high-capacity battery pack in a limited space inside an electric automobile, a structure change of a battery pack itself is required, and change of components forming the battery pack meeting this requirement is also required.